1. Technical Field
The present invention relates to input supporting methods of a variable name suitable for incorporation etc. to a program development supporting device of a PLC, and in particular, to an input supporting method of a variable name used when inputting a variable name as an operand of a command.
2. Related Art
Conventionally, an operand of a command (e.g., LD command, AND command, MOV command etc.) contained in a ladder program of a programmable controller (hereinafter referred to as PLC) is generally described with an address (which indicates the position in a memory where data handled in the program are stored, and which is represented with a digit sequence of a plurality of digits or with a character indicating the type of data added to the head of the digit sequence). When describing the operand with an address, devisal has been made to facilitate the understanding of the semantic content of each operand by adding a command to each address.
In recent years, the operand of the command can be described with a variable name including an arbitrary character string, and programming in variable base such as the high-level language of a personal computer is being actively pursued. In programming in variable base, the meaning of the address corresponding to the operand can be intuitively understood by describing the operand with a variable name, and a program excelling in maintenance can be provided.
If the operand is described with a variable name, the program can be easily reused even if change is made in the application of the address corresponding to the operand by simply changing the address to assign to the variable name (e.g., editing the table showing the correspondence of variable name and address) without changing the program.
Most operands in the ladder program of the PLC are often bit type (BOOL type), where a several thousand or, in some cases, a several tens of thousands of operands needs to be described in one program for the bit type operand.
If the variable name is used for the operand in such a case, the variable needs to be defined with a long character string so that duplication of the variable name does not occur, and so as to understand the meaning with the variable name. In other words, a digit sequence of about few words is required in a similar case if the address is used for the operand, whereas a character string of a few dozens of characters (e.g., alphabet string) is required if the variable name is used for the operand, and hence the input of the character string takes time and the efficiency of the programming is not satisfactory.
In order to enhance the programming efficiency, a function of searching the variable table with which the variable name is registered every time one character is inputted, narrowing down the character string of the target variable name, extracting that in which the character next to the confirmed character is the smallest in alphabetical order from the narrowed down variable names, and displaying the extracted character as a candidate of the variable name. Such a function is generally called an autocomplete function.